So-called chirped delay lines are used for analogue signal recessing, such as microwave pulse compressors, real time (instantaneous) spectrum analyzers, equalizers in fiber optical communication systems etc. There are several and different technical implementations of chirped delay lines. These are all characterized by uniform insertion losses and linear frequency dependence of the group delay, see [1], [2]. A simple prior art micro strip chirped delay line is disclosed in [1] and illustrated in FIG. 1 and FIG. 2. A prior art mechanically tunable delay line is reported in [2] and illustrated in FIG. 3.
In applications, such as equalizers used in optical communications systems, tunable chirped delay lines are required. The mechanical tunable delay line proposed in [2] is bulky, and not cost effective. Even though the tunable delay line proposed in [3] is simple, small, and cost effective, it has no chirped delay time features including linear frequency dependence of the delay time. The last two types of delay lines also suffer from impedance mismatch associated with tuning.
Consequently, there is a need for a tunable chirped delay line, which is small, simple, and cost effective and provide a reduced impedance mismatch as compared to the above mentioned prior art solutions.